<!DOCTYPE html>
<html>

	<head>
		<meta charset="utf-8">
		<title></title>
		<style type="text/css">
			* {
				margin: 0;
				padding: 0;
			}
			.main{
				width: 600px;
				height: 600px;
				border: 1px solid #999;
				margin: 0 auto;
				position: relative;
			}
			.box {
				height: 200px;
				width: 400px;
				background-color: #ccc;
				position: absolute;
				top: 50%;
				right: 50%;
				margin-right: -200px;
				margin-top: -100px;
			}
			
			.one {
				position: absolute;
				height: 50px;
				width: 50px;
				border-radius:0 0 100% 0;
				top:0;
				left: 0;
				background-color: #fc0;
			}
			.two{
				position: absolute;
				height: 50px;
				width: 50px;
				border-radius:100% 0 0 0;
				bottom:0;
				right: 0;
				background-color: #fc0;
			}
		</style>
	</head>

	<body>
		<div class="main">
			<div class="box">
				<div class="one">

				</div>
				<div class="two">

				</div>

			</div>
		</div>
	</body>

</html>